The Product Reviews tab will only display product review information once an ASIN has been selected to begin tracking.
All Seller Labs Pro subscriptions come with unlimited tracking. In most cases, tracking one child ASIN will pull in reviews for all variations of the product, so there's no need to track more than one variation.
To start tracking an ASIN:
Search for the product you want to track, and toggle the button to the left of the product in the product list.
Within a few hours, product reviews will begin to display in your Product Reviews page.